Arc Express was a project to build new rapid transit lines in île-de-France, in France. It was designed to satisfy the need for increased travel among the suburbs of Paris and to relieve the saturation of a number of radial lines, such as Métro Line 13 and RER Line A. Previous proposals for an orbital metro line, dating back to the early 1980s, ...Found on http://en.wikipedia.org/wiki/Arc_Express